The field of art to which this invention pertains is polysaccharide derivatives.
Polygalactomannans and their derivatives are well known polysaccharide compositions which have many uses as thickening agents in aqueous systems.
The polygalactomannans are polysaccharides composed principally of galactose and mannose units and are usually found in the endosperm of leguminous seeds, such as guar, locust bean, honey locust, flame tree and the like. Guar gum, for example, is composed mostly of a polygalactomannan which essentially is a straight chain mannan with single membered galactose branches. The ratio of galactose to mannose in the guar polymer is 1:2.
Locust bean gum is a polygalactomannan of similar molecular structure in which the ratio of galactose to mannose is 1:4. Guar and locust bean gums are the preferred sources of polygalactomannans, principally because of their commercial availability.
Hydroxyalkyl polygalactomannans are made by reacting the polygalactomannans with an alkylene oxide having at least two and, preferably, three or more carbon atoms as disclosed in U.S. Pat. No. 3,483,121. Polygalactomannans, as stated hereinabove, are composed of units of galactose and mannose sugars, each of which has an average of three hydroxyl sites. The alkylene oxide reacts with the hydroxyl groups to produce hydroxyalkyl ether derivatives. Each unit of alkylene oxide added to the polygalactomannan in turn adds a new hydroxyl group which is itself reactive. Theoretically, there is no limit to the amount of alkylene oxide which may be added to the polygalactomannan. As a practical matter however, a molecular substitution (M.S.) of about 4 or 5 is a practical upper limit.
Carboxyalkyl ethers of polygalactomannans are made by reacting the polygalactomannan with a halofatty acid or with acrylonitrile or methacrylonitrile followed by hydrolysis of the nitrile group to a carboxylic acid groups. Such carboxyalkyl ether derivatives contain one to three carbon atoms in the alkyl group and are described in a number of patents, examples of which are U.S. Pat. Nos.: 2,477,544; 2,520,161; 2,599,771; 3,679,658; 3,712,883; and 3,740,388.
Hydroxyalkyl ether-carboxyalkyl ether mixed derivatives of polygalactomannans are described in U.S. Pat. No. 3,723,408. The disclosed mixed derivatives contain three to eight carbon atoms in the hydroxyalkyl groups and two to four carbon atoms in the carboxyalkyl groups.
Polygalactomannans containing both hydrophilic and hydrophobic groups are disclosed in U.S. Pat. Nos. 4,870,167 and 4,960,876. In these patents, the hydrophilic groups are alkyl or hydroxyalkyl groups containing one to four carbon atoms or short alkyl chain carboxyl or amino substituents. The hydrophobic groups are substituents containing eight to thirty-two carbon atoms.